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Sound Desks
'Mixing console' A mixing console; also known as a audio mixer, sound board, mixing desk or mixer is one of the most fundamental pieces of professional audio equipment used in a broadcast system, because after all what is moving pictures without sound? A mixing console is an electronic device thats core function is to combine, or "mix" audio signals; mixing consoles can also allow a us to route signals to various outboards/ effects, change the level, or dynamics of audio signals. Mixing consoles have various applications, including recording studios, public address systems, sound reinforcement systems, broadcasting, and post production. 'The Basics' As mentioned above, a "mixer" combines signals from a number of separate sound sources, processes them to produce an acceptable balance and quality, and then passes the output mix on to a recorder, broadcast chain or PA system. Mixers are able to take a number of audio inputs, which are fed to input channels, each capable of handling signals at either microphone or line levels, (dependant upon the audio source). Mixers also have facilities in place to adjust levels and apply equalisation, and in addition may generate extra separately controlled mixes for outboard equipment such as effects units, or even mixes for foldback, cue feeds or multitrack recorders. It is also expected that a mixing desk provides a means of listening to and or metering the individual channels, so that controls can be adjusted on an artistic or technical basis. Most desks have a similar signal path: the input signal will be generated, from a microphone or line source, it will pass through the microphone amplifier or line buffer stage, where the signal level is optimised for headroom and noise performance; it then passes on to the equaliser, where frequencies of a signal can be cut or boosted; before reaching the channel fader. Auxiliary outputs will can be located before or after the fader, there may also be insert points where the signal can be patched from the desk, and processed externally (perhaps with a compressor, a noise gate, or even an effects unit), and then returned to continue through the desk. Next, the signal is routed to the available outputs or groups as appropriate. Groups are provided to make it easier to control a large number of signals, allowing user to apply a change to affect a collection of channel signals simultaneously. The signal then is able to be outputted from the desk, onto the its required destination. 'Channel strip:' Each signal that is input into the mixer has its own channel. Most mixing desks can accommodate stereo or mono audio signals. On most mixers, each channel has an XLR input, and many have RCA or quarter-inch Jack plug line inputs. The channel strip usually consists of: '- Inputs, typically XLR or ¼ inch jack (located at the rear of the desk)' '- Input jacks / microphone preamplifier' '- Basic input controls (eg. gain)' '- Channel EQ (High, Mids and low)' '- Routing Section including Direct Outs, Aux-sends, Panning control and subgroup or “BUS” assignments' '- volume Faders' 'Basic input controls' Below each input there are a number of rotary controls that an engineer/ operator can adjust to tweak the input signal. The first available are often the gain or trim control; the input signal from the external device can be assessed at this point, and using the trim/ gain control an engineer or operator can asses the amount of amplification or attenuation needed to bring the signal to the optimum level for processing. It is at this point that noise can be introduced to a signal, due to the amount of gain being introduced (around 50db + for a microphone). Balanced inputs and connectors, such as XLR or quarter-inch jack connectors, are often used as they reduce interference problems. 'Channel equalization' Further down the channel, are controls affect the equalization (EQ) of the signal. This is achieved by separately attenuating or boosting a range of frequencies, e.g., bass, midrange, and treble. Most large mixing consoles (24 channels or more) usually have sweep equalization controls on one or more bands of its parametric equalizer on each channel, meaning the frequency and affected bandwidth of equalization can be adjusted.Smaller mixers often have fewer e.q controls, and some mixers have a general equalization control (either graphic or parametric) at the output. 'Channel Faders' Each channel on a mixer has an potentiometer, controlled by a sliding volume control, which is often refereed to as a fader. The fader allows threadjustment of the level, or amplitude, of that channel in the final mix. A typical mixing console has many rows of these sliding volume controls. Each control adjusts only its associated channel; therefore, it only affects the level of the signal from one microphone or other audio device that has been assigned to that channel. The PFL button is often located just above the faders and below the eq strip, this allows the operator to be listening to the audio signal independent of fader position, while adjusting the equalizer. 'Miscellaneous controls on a channel strip' Other controls that may be found on a mixing desks' input section include a phantom power switch in order to power condenser microphones, a phase-reverse switch which allows the polarity of the input signal to be reversed, a ground lift switch, which disables pin one on the XLR connector from the console's audio ground bus, useful in eliminating hum and other undesired noise, and a mute switch, which allows the audio signal to be instantly "turned off" at the push of a button. 'Optional Outputs:' The audio signal, having been adjusted both at the equalizer and input fader sections, can be sent to a series of outputs determined by a series of button settings to subgroups, post-fader auxiliary outputs, or other outputs. Auxiliary sends will usually be found on every input channel which allow the input signal in question to be routed to different outputs at a given proportional level; if the send in question is post-fader, the amount of the signal routed to that particular auxiliary send will be based on the level of the fader and the position of the auxiliary send knob. If the send in question is pre-fader, the amount of signal routed to that particular auxiliary send will be based solely on the auxiliary send knob. The benefit of using an aux send is that it enables the signals from mutiple channels on a mixing console to be simultaneously routed to a single outboard device. For example, audio signals from all the channels of a 24 channel mixing console can effectively be routed to a reverb unit so that all channels can have reverb applied simultaneously. Another practical application for aux sends is to facilitate on-stage fold back. The aux sends from a group of inputs can also be routed to an amplifier and then sent to monitor speakers so that onstage musicians can hear their performance. Auxillary sends are usually used for routing inputs to effect proccesors, or to facilitate stage fold-back. 'Pan' A “pan” control is short for panoramic potentiometer, which allows the audio signal to be proportionally routed between two different outputs, usually (left or right). It is this knob that provides studio engineers with the flexibility to change a input place in the stereo image, i.e. not all the way left, not all the way right, and not directly in the centre. 'Digital Desks' Digital Desk represent a completely different challenge in terms of operation. Digital desks physically don't look too dissimilar to that of an analogue desk, in the sense that; there are still channel strips with a array of dials and a volume fader at the bottom. However the main difference between analogue desks and digital desks is the way in which it operates and the way in which audio signals are processed. A digital console opens up a new world of options for working with your inputs and outputs. Due to the fact that it is software driven, the user is really in full control of the system as they can decide how they want to interface with everything. Most digital mixers are designed to look and have the ability to function much like an analogue mixer; they have faders, channel strips, and many similar layout features; the difference however, is that all of those items are programmable, and can be set to control whatever you want them to control. A digital console allows you to program everything, including levels, and save them for recalling at a later time, as well as allowing for a massive number of inputs to be connected and accessed/ arranged through digital input layers. Although you are limited as to how many you can quickly control once you’ve exceed the number of channel strips available (due to the layers). It is important to note that no audio system is completely digital as the original signal being input into the system would have derived from an analogue source. Once the analogue signal reaches the mixer, it is then converted again into a digital signal. The digital signal is essentially the language known as binary; it is a language that computers use in their processing and functioning. ''' '''This converted signal allows for a completely different interface to that of an analogue signal, as software can be used to manipulate the signal as opposed to individual knobs and faders. In order to maintain a familiar interface for operators, digital consoles are used and set out in a way to resemble analogue desks. For example, you could simply use a computer screen with a software based mixer board and just click and drag your settings to whatever you want. The digital signal is manipulated to whatever output is desired, and is then output in either digital form for further processing, or else is re-converted back into analogue to be played through speakers or analogue outboard equipment. An analogue signal is required as the ultimate output from the speakers, as our ears hear only analogue sound waves generated from sound pressure waves. Another key element that defines the make up of a digital mixing system is remote mixing. In most professional installations in broadcasting, only the equipment intended to have a direct user interface for example the control surface and outboard equipment, and the patch bays to support the equipment are present in the studio, often the backbone of the system, I.e the digital mixer itself is located in a separate room for example in CAR, and is connected via ethernet cable. An important difference to note with digital mixers is that while analogue travels without delay, there is an unavoidable amount of latency involved with digital mixers. This latency (delay) is caused by the conversion processes between digital and analogue, and can be measured typically in a matter of milliseconds. This latency can be unnoticeable in live events, but can be catastrophic in the broadcast environment as latency causes synchronising issues. Professional digital recorders do not suffer from this because they run off an internal clock that aligns the tracks perfectly. '' ''Advantages: ▪ There is no added noise, (unintentional) distortion, or other signal degradation while the signal is in the digital domain. ▪ Aux sends can be mixed on the main faders rather than on a row of potentiometers. ▪ Signal routing is often much more flexible than with an analog-based console. ▪ The setup of the console can be saved and loaded at will. This is particularly useful in live events where a setup for each band can be largely prepared in advance, saved, and then loaded as needed. ▪ There are typically many on-board effects and virtual signal processors available, eliminating the need for additional hardware. Disadvantages: ▪ The number of faders is often far less than the number of input channels. The extra input channels are not accessible until a bank/layer of faders is switched to control them. ▪ Digital conversion and processing adds latency, or delay, into the signal. ▪ The act of making adjustments is often slower for compact digital mixers which require the user to page through one or more layers of commands before reaching the desired control. 'So which do you choose?' Digital consoles are more expensive, more time consuming and difficult to learn/master/teach, and carry with them an inherent potential to crash. That being said, they also allow for a massive amount of inputs, an incredible level of interfacing and control, a cleaner signal, and the ability to program settings for different purposes, save them, and recall them whenever you need them. Analogue consoles on the other hand are much less expensive in comparison, much simpler to learn/master/teach, and will only crash if the power goes out. The cons remain basic: analogue boards are unable to save their settings to be recalled, and they will always emit some amount of noise that will be heard through the speakers (though all sound professionals will agree that this amount is typically non-existent to the human ear, and more noise tends to be emitted from the other electronic equipment used, like the amplifier for example). Overall from a operators point of view, I prefer digital mixing consoles as this is vastly becoming the industry standard and the versatility of the digital consoles make them the first choice for audio engineers. 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